Funky Shading After Boolean
It looks like it's both a topology and a Weighted Normal modifier problem:


You should avoid tris if they are twisted and stretched, so you should correct your topology with quads.
I don't know a lot about Weighted Normal modifier, here is an explanation by Cgslav on how it works, it looks like it's mainly made for bevel, I'm not sure it's made to fake a smooth shape like yours, rather use Subdivision Surface if you can, or add a bit of geometry?